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Determine the concentration of a limewater solution.

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Introduction

Determine the concentration of a limewater solution. Through a titration experiment I aim to find the concentration of a sample of limewater. I will have 250cm of limewater, which contains approximately 1g dm of calcium hydroxide. I am using a strong acid with a weak base. The acid is a 2.00 mol dm solution of hydrochloric acid. The equation for this reaction follows: Ca(OH) (aq) + 2HCl CaCl (aq) + 2H 0 (aq) The acid is such a concentrated solution that only a few drops would cause the calcium hydroxide to be converted into calcium chloride, and this would result in a high % error deeming my results very unreliable. To improve this situation I need to calculate the molarity of the calcium hydroxide and change the concentration of the hydrochloric acid so that there is an appropriate ration between the two substances. To do this I will need to use the following formula equation. No. of moles = Mass given Mass of one mole So if we work through this, the mass given is 1. Now the relative atomic mass of calcium hydroxide is needed, and this is: Ca(OH) = 40.08+(16x2)+(2x1) = 1 74.08 = 0.01 moles dm The calcium hydroxide has a concentration of 0.01 mol dm , but we have to look at the ratio these two are in from the equation. ...read more.

Middle

In your results table the initial reading needs to be recorded to 0.05. 5. 10cm of limewater needs to be put into a clean conical flask. This can be achieved most accurately using a pipette filler. To the limewater three drops of methyl orange need to be added. 6. Put the conical flask containing the limewater directly under the tip of the burette. Beneath the conical flask a tile also needs to be placed, so that any colour change is more noticeable. 7. Carefully allow 1cm of the diluted HCl to run into the conical flask at a time, after each cm close the tip and swirl the conical flask around. When the solution changes colour record the volume that this occurs at in your results table. 8. Dispose of the contents of the conical flask. Measure out another 10cm of limewater and place in the conical flask along with three more drops of methyl orange. 9. Continually allow HCl to run into the conical flask to a volume that's within 3cm of the volume used before, then add 0.05 at a time until the solution changes colour. Record the initial and final volumes in your results table. 10. Repeat this experiment until you have three volumes that are within 0.1cm of each other. ...read more.

Conclusion

The burette, pipette and volumetric flask all share the approximate accuracy of 0.05cm . So any error that may have occurred during the experiment isn't likely to be connected to the equipment, although it still needs to be considered. The limitation which, has the biggest effect on the results I think, is human error. Each time we complete a titration we have to judge the colour of the solution and whether it's reacted. It's possible for our perceptions of this colour to change, and we might also be influenced by the result we achieved last and feel it's changed so that our results are similar. One way I've already tried to counteract this problem is to dilute the strong concentration of acid, so that the colour change is more gradual and easier to judge. Another method of achieving this is to use a computer with a camera, after the first titration a picture could be taken so that during the next titration you can compare, which should leave you with near identical colours. Another way to improve this experiment includes repeating the titrations more than three times so that an average of more results could be worked out. The consistency of my results supports the claim that they are reliable. While there are some improvements to be made, within the confinements of school supplies I think I carried out the assessment appropriately. ...read more.

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